# Photo-excited extracellular electron transfer of electroactive microorganism triggers RAFT polymerization

## TL;DR

Scientists used bacteria to trigger a type of polymerization that can create materials with consistent quality and diverse uses.

## Contribution

A new system using electroactive bacteria to initiate RAFT polymerization without end-group heterogeneity.

## Key findings

- Shewanella oneidensis-secreted flavins act as electron shuttles to reduce chain transfer agents and generate radicals.
- Genetic engineering of S. oneidensis improved flavin production, achieving high polymer conversion and low polydispersity.
- The system works with various monomers and CTAs, enabling synthesis of diverse block copolymers.

## Abstract

Living cell-triggered reversible addition-fragmentation chain-transfer (RAFT) polymerization is of great value for construction of living materials with diverse applications. However, microorganisms-activated polymerization without end-group heterogeneity is not yet established. Here, we develop an electroactive microorganism-triggered polymerization system using Shewanella oneidensis-secreted flavins (as electron shuttles) to directly reduce chain transfer agents (CTAs) to continuously generate radicals, thus initiating RAFT polymerization. This S. oneidensis-triggered polymerization integrates microbial extracellular electron transfer pathway and photoinduced electron transfer to reduce CTAs for continuous radical generation. We then genetically engineer S. oneidensis to enhance flavins biosynthesis and transport, accomplishing increased conversion ratio ( > 90%) of poly(N, N-dimethylacrylamide) with low polydispersity (Ð < 1.20). In addition, the S. oneidensis-triggered RAFT polymerization is effective for various monomers and CTAs, being able to synthesize diverse block copolymers. Synergistic integration of synthetic biology and RAFT polymerization provides a sustainable and controllable polymerization platform.

Living cell-mediated reversible deactivation radical polymerization is valuable for the construction of engineered living materials, but microorganisms-activated reversible addition-fragmentation chain transfer (RAFT) polymerization without end-group heterogeneity was not yet established. Here, the authors develop an electroactive microorganism-triggered RAFT polymerization system using Shewanella oneidensis-secreted electron shuttle flavins as the electron mediators to directly reduce chain-transfer agents to continuously generate radicals, thus initiating RAFT polymerization.